The invention relates generally to permanent magnet materials, methods of making permanent magnet materials, and electromagnetic devices including permanent magnet materials.
Many types of electromechanical energy converters such as motors, generators, and actuators use permanent magnets to create an open circuit flux density which interacts with a field created by an electric circuit to provide torque. To a large extent, the size and efficiency of a converter of a given power rating is determined by the xe2x80x9cenergy densityxe2x80x9d of the magnet in the device. The higher the open circuit air gap flux density produced by the magnet, the more torque that can be produced per unit weight and the higher the motor efficiency for a given power input. Open circuit flux is determined by the strength of the magnet and the effective length of the air gap. The stronger the magnet and the smaller the effective air gap, the more efficient and smaller the machine.
As a practical matter, cost savings can be achieved by making the magnets as thin as feasible while providing a sufficient thickness to prevent demagnetization from armature reaction flux density. As compared with thicker magnets, thinner magnets require less space. However, the permanent magnets are typically designed to be thick so as to avoid experiencing an operating point that might result in demagnetization. For example, magnet thicknesses for 373 Watt (one-half horse power) motors typically range from about 2.54 millimeters (about 0.1 inches) to about 7.62 millimeters (about 0.3 inches).
It would be desirable to have a permanent magnetic material not constrained by conventional thicknesses and having high residual magnetization and large intrinsic coercive force.
Briefly, in accordance with one embodiment of the present invention, a permanent magnet comprises: iron-boron-rare earth alloy particulate having an intrinsic coercive force of at least about 1591 kiloamperes/meter (about 20 kiloOersteds) and a residual magnetization of at least about 0.8 tesla (about 8 kiloGauss), wherein the rare earth content comprises praseodymium, a light rare earth element selected from the group consisting of cerium, lanthanum, yttrium and mixtures thereof, and balance neodymium; and a binder bonding the particulate.
In accordance with another embodiment of the present invention, a method of fabricating at least one permanent magnet comprises: providing iron-boron-rare earth alloy particulate having an intrinsic coercive force of at least about 1591 kiloamperes/meter (about 20 kiloOersteds) and a residual magnetization of at least about 0.8 tesla (about 8 kiloGauss), wherein the rare earth content comprises praseodymium, a light rare earth element selected from the group consisting of cerium, lanthanum, yttrium and mixtures thereof, and balance neodymium; providing a binder; bonding the particulate with the binder to provide moldable particulate material; and molding the at least one permanent magnet from the moldable particulate material.